I see a whole bunch of online pitch rate calculators such as this one by Brewer's Friend, but I'm struggling to find the actual formula(e) used under the hood by them.

Does anybody know of any generally-accepted pitch rate formulas out there? Ideally I'd like to know what Brewer's Friend is using but I'll take anything thats in the ballpark.

2 Answers 2


If you view the source of the BF website, there is some packed javascript in there that you can run through an online tool to pretty-print some mathematical calculations used on the site.

I've tried using those pitch rate calculators but so much of it is guesswork that it just seems pointless. I have no idea how many billion cells (slurry density) I have in my harvested yeast.

When I harvest my yeast, I pour it into three 16oz mason jars. I like to leave about an inch of beer at the top as a vapor barrier when storing in the fridge.

When I make beer, a few days prior I'll pull out a jar of slurry and give it a whiff. If it smells good, I'll make a starter and let it whirl on the stir plate a couple days. If the starter smells ok, I'll decant what I can and pitch the rest in my wort. I can usually see fermenter activity within a couple hours, depending on the temp.

Sometimes tools come along which add more drudgery and very little benefit. Whether the pitch tool is one of these, I don't know. For me though, I like to keep the rules simple and see what I can get away with. I want to have fun and make enjoyable beer.


Common advice says 0.75 million cells/ml/°P for ales and 1.5 million cells/ml/°P for lagers. However more modern breweries are upping these numbers just a bit.

I can say that calculations really only work when you're using a hemacytometer to measure cell count. Any eyeballing or using cell counts on yeast packaging- the math is all out the window.

  • Always wondered hth anyone was measuring cell count 👍
    – HomeBrew
    Oct 13, 2021 at 11:38
  • @HomeBrew There's some dilution methods where you can get relatively close with naked-eye testing. I do remember a reddit user (a sharp biologist who now runs The Yeast Bay yeast bank) spread around a naked-eye method that worked pretty good. This is the link, and scroll down for the comment from /u/biobrewer YEAST COUNTING BY DILUTION .
    – rob
    Oct 13, 2021 at 13:09
  • 1
    Cool info! There's a lot there to digest but the method of eyeballing turbidity to equite cell count seems practical enough.
    – HomeBrew
    Oct 13, 2021 at 16:41

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